In electric power transmission and distribution networks, fault current conditions may occur. A fault current condition is an abrupt surge in the current flowing through the network caused by faults or short circuits in the network. Causes of the faults may include lightning striking the network, and downing and grounding of the transmission power lines due to severe weather or falling trees. When faults occur, load appears to be reduced instantaneously. The network, in response, delivers a large amount of current (i.e. overcurrent) to this load or, in this case, the faults. This surge or fault current condition is undesirable as the condition may damage the network or equipment connected to the network. In particular, the network and the equipment connected thereto may burn or, in some cases, explode.
One of the systems used to protect power equipments from damages caused by fault currents may be a current limiting reactor. Referring to FIG. 1, there is shown a portion of the power transmission and distribution network 100. As illustrated in the figure, the network 100 may comprise a network equipment 102. Herein, the network equipment 102 may be a transformer, a power generator, and/or any other component that may be connected into the network 100. To reduce or prevent the fault current from flowing into and damaging the equipment 102, a current limiting reactor 104 may be serially connected to the network equipment 102. In some embodiments, the network equipment 102 may be a power source and the current limiting reactor 104 may be disposed downstream of the network equipment 102. In other embodiments, the network equipment may be a power sink and the current limiting reactor 104 may be disposed upstream of the network equipment 102. As the name implies, the current limiting reactor 104 may have high resistance or impedance, or both, to limit the amount of current flowing into or out of the network equipment 102 during the fault condition.
Although connecting the current limiting reactor 104 to the network equipment 102 may protect the equipment 102 during the fault condition, the reactor 104 has many disadvantages. Among others, the current limiting reactor 104 may also limit the amount of voltage available to the network equipment 102 during the normal operation. If the power network is a constant voltage network, this voltage loss must be compensated for through the use of capacitors, dynamic volt ampere reactive (VAR) compensators, or other means. These systems also can change the phase angle of the power, causing difficulty in transmitting real power to the end user. As such, great amounts of power are lost during normal operation. For example, as much as 3% of the power is lost due to the reactor 104. To compensate for this loss, additional current or power must be generated. Generating additional current or power may place undue financial burden on the power generator and/or power distributor and, ultimately to the power consumer.
As such, a new technique for limiting transmission of fault current is needed.